Soft Condensed Matter
Real-time quantification of fluid flows around bubbles during directional solidification
Bastien Isabella, Emma Houllegatte, Cécile Monteux et al. (+1 more)
Directional solidification of bubbly
liquids plays a critical role in shaping the microstructure and properties of many materials, yet the fluid dynamics governing bubble behavior during solidification remain poorly understood. Using cryo-confocal microscopy and particle image velocimetry, we quantify fluid flows around bubbles during solidification of water containing surfactants and tracers. Our results reveal that volumetric expansion dominates fluid motion, with velocities scaling linearly with the solidification rate (1-20$~\mu m/s$), while Marangoni flows-hypothesized to play a key role-are negligible ($< 5~\mu m/s$) under our experimental conditions. Diffusiophoresis and thermophoresis also contribute minimally. These findings challenge existing theoretical models and provide a framework for controlling bubble distribution in solidified materials
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All authors Bastien Isabella, Emma Houllegatte, Cécile Monteux, Sylvain Deville
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Interference of critical dynamics associated with zero modes
Zhi-Han Zhang, Han-Chuan Kou and Peng Li
We study the interference of critical dynamics associated with zero modes (ICDZM) in the generalized Creutz ladders using closed quench paths that pass through two critical points successively. By reading out the final zero-mode transfer probability, we find rich ICDZM interference patterns dependent on the quench path. In particular, when the closed path links two topologically nontrivial phases, the ICDZM pattern may either vanish or exhibit period doubling. Within the framework of WKB analysis, this phenomenon is well clarified by the interference phase accumulated in the quench procedure. We also demonstrate that the zero-mode transfer probability can be detected by the deviation of the boundary particle number from its initial fractional value, which arises from the blending of bulk modes in the critical dynamics. As an edge defect, the zero-mode transfer probability captures both the ICDZM oscillation and the known anomalous defect production in a non-closed quench path. These results identify ICDZM and the corresponding edge defect as probes for critical dynamics associated with topological zero modes.
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Other Condensed Matter
Transformation of the gyrotropic mode spectrum of the FM / AFM disk via vortex imprinting
E. V. Skorokhodov, E. A. Karashtin, I. A. Fedotov et al. (+2 more)
We experimentally investigate the
magnetic gyrotropic mode in a system of
vortex ferromagnetic (FM) nanooscillator exchange coupled to an
antiferromagnetic (AFM) layer. The micron-sized disks formed from the $Ni_{80}Fe_{20}$ (12 nm) / $Ir_{80}Mn_{20}$ (5 nm) FM/AFM
heterostructure are prepared so that the
vortex magnetic state is imprinted into the AFM layer. We apply a
magnetic resonance force microscopy (MRFM) method to locally study
magnetic oscillations in single FM/AFM disks. We show that the gyrotropic mode frequency is significantly (approximately four times) shifted to the high frequency range compared to a similar structure consisting of a single
ferromagnetic disk. Upon applying an in-plane
magnetic field, we observe a strong peak at a double frequency which was previously predicted in theory. This shows that nonlinearity in
vortex dynamics is strongly enhanced in the FM/AFM system under investigation. Thus the
magnetic imprinting technology reveals great potential for future application in high-frequency spintronic devices.
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All authors E. V. Skorokhodov, E. A. Karashtin, I. A. Fedotov, I. Yu. Pashen'kin, M. V. Sapozhnikov
Materials Science
Decoding Crystallographic Surface Chirality from Real Space and Momentum Space Images by Machine Learning
Chetana Badala Viswanatha, Ka Man Yu, Benito Arnoldi et al. (+6 more)
Intrinsically
chiral metal surfaces, where handedness arises from the asymmetric step-kink-terrace
topology of high-Miller index planes, are model systems for enantiospecific catalysis, sensing, and spintronics. Yet no consistent method exists to classify their handedness directly from experimental observables, without prior knowledge of crystallographic indices. Here, we report a dual-domain machine learning framework that recognizes handedness in
chiral metal surfaces from two independent image representations: atomic structure models in real space and simulated momentum-resolved photoemission maps of
Fermi surface projections in reciprocal space. A ResNet18 model pretrained on general image data is fine-tuned for chirality classification independently on both image representations and achieves meaningful classification accuracy for both real space and reciprocal space images. However, the
Fermi surface classifier significantly outperforms the real space classifier. Critically, the reciprocal space classifier, trained only on synthetic images, correctly identifies synchrotron-acquired experimental Angle-Resolved Photoemission Spectroscopy (ARPES) maps of Cu(643)$^R$ and Cu(643)$^S$. The stronger performance in momentum space, as well as the transfer to experimental data, shows that handedness is encoded more globally and robustly in the electronic structure than in the spatially localized kink-site geometry. These results establish ARPES as a quantitative readout of crystallographic surface chirality and suggest a scalable route to identify
chiral metal surfaces relevant to
spin-selective phenomena.
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All authors Chetana Badala Viswanatha, Ka Man Yu, Benito Arnoldi, Anagha Aravind, Aaruni Kaushik, Jannis Lessmeister, Martin Aeschlimann, Benjamin Stadtmüller, S. Harshini Tekur
Materials Science
A first-principles approach for predicting infrared optical properties of solids
Sreerag Sundaram, Ziqi Guo, Dudong Feng et al. (+2 more)
We present a simplified formalism for predicting infrared optical constants from first-principles calculations. Addressing limitations of the widely used four-parameter semi-
quantum Lorentz model, the proposed approach bridges the gap between the harmonic three-parameter model and full self-energy-based methods. By incorporating essential anharmonic effects including four-
phonon scattering and
phonon renormalisation, the model provides an efficient and accurate alternative while maintaining low computational cost. The frequency-dependent refractive indices of MgO and rutile TiO$_2$ are computed and compared with experimental data, demonstrating good quantitative agreement. The framework offers a practical approach for predicting optical properties of materials across a wide range of materials.
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All authors Sreerag Sundaram, Ziqi Guo, Dudong Feng, Karthik Sasihithlu, Xiulin Ruan
Materials Science
Disentangling the origin of degradation in perovskite solar cells via optical imaging and Bayesian inference
Akash Dasgupta, Robert D. J. Oliver, Manuel Kober-Czerny et al. (+5 more)
Machine learning and computational inference, coupled with experimental data, promise to significantly accelerate our rate of learning in most scientific disciplines. In this study, we develop tools that connect microscopic observations to macroscopic device behaviour, a capability that is essential for accelerating the design of durable energy materials. To this end, we introduce a novel approach that integrates photoluminescence imaging with drift
diffusion simulations to understand operation and degradation in fully fabricated perovskite
solar cells. By employing
Bayesian inference, we generate "inferred maps" of parameters that govern recombination processes present in devices. We track these parameter maps while the devices are aged (70 {\deg}C, full spectrum sunlight) to analyse their temporal
evolution during degradation. Notably, our approach allows us to distinguish between degradation occurring at the hole or electron transporting layer interface, or within the bulk. Our analysis reveals pronounced spatially non-uniform degradation, with significant macroscopic heterogeneity observed in the optoelectronic parameter maps. We pinpoint the greatest degradation observed in specific regions to stem from the perovskite/transport layer interfaces. Finally, we demonstrate that an amino-silane molecular passivation treatment suppresses this degradation, highlighting its specific role in enhancing device stability. Our approach offers valuable insights for future device fabrication and is a clear exemplification of how advanced
Bayesian inference can significantly increase the value of experimental data.
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All authors Akash Dasgupta, Robert D. J. Oliver, Manuel Kober-Czerny, Charlie H. G. Nicholls, Xueli Cao, Yen-Hung Lin, Alexandra J. Ramadan, Henry J. Snaith
Statistical Mechanics · Cross-listed from math-ph
Chiral Long-Range Order in three Euclidean Lattice Gross-Neveu Models
Simone Fabbri and Leonardo Goller
We prove the existence of Long-Range Order in a class of two-dimensional Euclidean
lattice Gross-Neveu models with an even number of
fermion flavors, covering three standard
lattice discretizations, including naive and staggered
fermions widely used in numerical studies. By performing a Hubbard-Stratonovich transformation, we map the fermionic systems to bosonic ones and establish Reflection Positivity for the resulting measures. Exploiting this structure, we combine Chessboard Estimates with a Peierls-type contour argument to prove Long-Range Order for the chirally charged
fermion-mass bilinear $\overline{\psi}\psi$ at sufficiently small coupling and sufficiently large
flavor number. Our analysis is robust with respect to the choice of
lattice discretization and applies uniformly across different realizations of the same underlying continuum model. Moreover, we obtain uniform pointwise bounds on the bosonic two-point function, equivalently on the fermionic mass-mass correlator, showing that it is quantitatively controlled by the minimizers of the effective potential. This provides a fully rigorous and non-perturbative demonstration of Long-Range Order in
lattice Gross-Neveu models and establishes a direct connection between the rigorous theory and its large-$N$ (mean-field) predictions.
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Materials Science
Holonomy Analysis of Optical-polarization Temperature Trajectories in Stress-induced Ferroelectric SrTiO$_3$
Hirotaka Manaka, Kazuma Seike and Yoko Miura
We develop a data-induced
geometric framework for temperature trajectories in optical-polarization data and apply it to temperature-dependent birefringence imaging of stress-induced ferroelectric SrTiO3. By treating the measured response as an observable projection of local material states, the optical-polarization response at each pixel is cast as a trajectory along the temperature axis. Singular value decomposition separates trajectory-induced
geometric objects associated with optical-polarization-direction structure and temperature-
evolution modes. Holonomies are then defined by transporting these objects around closed loops in real space. The resulting maps reveal spatially localized connection mismatches correlated with an enhanced ferroelectric transition temperature and stress-related optical anisotropy. Local order parameters and angular-gradient analyses confirm that these loop-level signals are distinct from orientational disorder and simple spatial variation. The signed holonomy of the temperature-
evolution modes further resolves positive and negative connection structures under a fixed frame convention. These results demonstrate that the data-induced connection geometry of temperature trajectories provides an experimentally accessible diagnostic of electromechanical inhomogeneity in SrTiO3 under stress, without explicitly reconstructing hidden strain or electric-polarization fields.
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Quantum Gases · Cross-listed from quant-ph
Fibonacci Steady-States and Persistent Oscillations in an Ordered Multimode Dicke Model
Miriam J. Leonhardt, Kai Müller, Oliver Lunt et al. (+1 more)
Ultracold atoms in multimode optical cavities provide a rich testbed for many-body phenomena enabled by light-mediated interactions. Recent experiments include realizations of
spin glasses and associative
memories, as described by multimode Dicke models with disordered couplings. However, the properties of multimode Dicke models with ordered coupling geometries remain largely unexplored. In this work, we investigate the stable steady-states of the multimode Dicke model with an ordered nearest-neighbor coupling geometry, where $n_c$ atomic clusters are coupled via $n_c-1$ cavity modes. We show that the number of mean-field stable steady-states in the superradiant phase exhibits Fibonacci scaling with the number of atomic clusters, and that a subset of these steady-states exhibit persistent oscillations. Using both the truncated Wigner approximation and the numerically-exact hierarchy of pure states, we further demonstrate that these features of the stable steady-state solutions persist for finite cluster sizes. Ordered multimode Dicke models, such as the nearest-neighbor coupling geometry considered here, are accessible with current experimental technologies and point toward a broader class of strongly interacting dissipative systems with similarly rich behavior.
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All authors Miriam J. Leonhardt, Kai Müller, Oliver Lunt, Andrew J. Daley
Soft Condensed Matter
Collective alignment controls rotation frustration in granular flows of elongated particles
Antonio Pol, Riccardo Artoni and Patrick Richard
Dense granular flows made of elongated particles exhibit a strong inhibition of particle rotation compared to spherical grains, but the mechanisms responsible for this effect remain unclear. Using three-dimensional discrete element simulations, we investigate the angular dynamics of elongated particles in dense, confined shear flows. We systematically vary particle aspect ratio, interparticle friction, and boundary conditions to elucidate their respective roles. We show that the reduction of the average angular velocity cannot be attributed to particle shape, friction, or solid fraction alone. Instead, it is controlled by the degree of collective
alignment developed under shear, quantified by a nematic order parameter. Based on this observation, we propose a simple scaling law linking the average angular velocity to the local shear rate through a hampering parameter that depends solely on the orientational order via the nematic order parameter. This scaling successfully collapses data obtained for different particle properties (shape, friction), different flow patterns, and, remarkably, remains valid for two additional flow configurations.
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Disordered Systems and Neural Networks
A solvable model for unsupervised federated learning
Giovanni Catania, Aurélien Decelle, Gianluca Manzan et al. (+2 more)
We introduce a theoretical framework for analyzing
federated learning in a generative setting through a teacher-multiple interacting students scenario, in which each student receives a distinct realization of the data, either through a different noise corruption or by accessing a different subset, possibly of varying size. Using theoretical tools in
equilibrium disordered system, we analytically show that interactions among students systematically enhance learning performance: highly noisy students require fewer samples to recover the underlying pattern, while low-noise students achieve a larger overlap with the ground-truth signal. We derive the optimal
Bayesian conditions for teacher recovery as functions of the sample complexity, noise level, and interaction strength, and validate these predictions through numerical simulations. The resulting dynamics can be mapped onto
equilibrium sampling in a Restricted Boltzmann Machine with a structured hidden layer, providing a principled theoretical understanding of how interactions improve distributed generative modeling.
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All authors Giovanni Catania, Aurélien Decelle, Gianluca Manzan, Beatriz Seoane, Daniele Tantari
Materials Science
A Geometric Design Principle for $\mathbb{Z}_2$ Topological Phases in Twisted Triangular-Lattice Bilayers
Jiaheng Li, Jiaxuan Liu, Yan Zhang et al. (+3 more)
Twisted van der Waals
bilayers provide a versatile platform for moiré electronic states, yet a transferable
symmetry-based principle for time-reversal-invariant $\mathbb{Z}_2$ moiré bands has remained largely missing. Here we show that triangular-
lattice bilayers with
symmetry-related stacking minima provide a
geometric route to an emergent honeycomb moiré
lattice. Band-edge states derived from the untwisted $\Gamma$ valley are trapped by the reconstructed stacking landscape, forming A/B moiré orbitals whose inter-domain coupling generates Dirac crossings.
Spin–orbit coupling opens a topological gap, yielding an effective Kane–Mele description and a
quantum spin Hall phase characterized by a nontrivial $\mathbb{Z}_2$ invariant. First-principles calculations for Janus BiTeBr confirm the robustness of this phase over a broad twist-angle range and demonstrate an electric-field-driven topological transition. Representative triangular-
lattice bilayers further establish this
symmetry-based design principle as a broadly applicable route to tunable moiré
quantum spin Hall materials.
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All authors Jiaheng Li, Jiaxuan Liu, Yan Zhang, Zhong Fang, Hongming Weng, Quansheng Wu
Quantum Gases · Cross-listed from quant-ph
Experiment-compatible measurement–feedback quantum state preparation with reinforcement learning
Xiaotian Nie, Tao Zhang and Linghui Chen
Ground-state preparation is a critical task in
quantum simulation and
quantum computing, as it enables the study of correlated phases and the generation of entangled resource states. While measurement–feedback control has emerged as a promising route to state preparation, existing schemes either rely on handcrafted, task-specific policies or are designed using full
quantum-state information that is unavailable in real experiments and becomes impractical for large many-body systems. Here we develop an adaptive measurement–feedback protocol based on reinforcement learning under partial observability. The controller uses only the history of experimentally accessible measurement outcomes to choose both the measurement operator and the feedback action in real time. To make training compatible with experiments, we introduce a
stochastic terminal reward built from one-shot measurements of randomly sampled
Hamiltonian components, avoiding unphysical full-state reconstruction while remaining an unbiased
estimator of the target energy. We demonstrate the method by preparing ground states of the Bose–Hubbard model and by generating GHZ states, establishing a scalable and hardware-compatible route to
quantum state preparation.
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Materials Science
Observation of orbital-angular-momentum-driven temperature modulation via the spin Peltier effect
Sang J. Park, Tsuneyoshi Kan, Takamasa Hirai et al. (+1 more)
Angular-momentum transport provides a pathway for controlling energy flow in solids beyond conventional charge-based mechanisms. While
spin currents are known to mediate
spin-caloritronic phenomena such as the
spin Peltier effect (SPE), the role of orbital angular momentum in heat transport remains largely unexplored. Here we demonstrate orbital-angular-momentum-driven temperature modulation via the SPE in yttrium iron garnet/Pt/CuOx
heterostructures. Using wedge-shaped CuOx layers combined with spatially resolved active thermal measurement techniques, we map the continuous thickness dependence and quantitatively disentangle the
spin- and orbital-current-mediated contributions within a single device. The orbital-mediated component exhibits a pronounced maximum at an intermediate thickness, revealing a characteristic length scale for interfacial orbital-angular-momentum generation and propagation at the Cu/CuOx interface. These results provide direct experimental evidence that charge-current-driven orbital angular momentum can drive SPE-induced temperature modulation, establishing interfacial orbital processes as an additional channel for heat transport and providing a pathway toward
spin-orbit caloritronics.
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All authors Sang J. Park, Tsuneyoshi Kan, Takamasa Hirai, Ken-ichi Uchida
Mesoscale and Nanoscale Physics
A micromagnetic model with bidirectional magneto-thermal coupling
Peiru Yi, Zian Xia and Weichao Yu
Most conventional micromagnetic frameworks in
spin caloritronics rely on a unidirectional coupling approximation, wherein thermal fluctuations drive magnetization dynamics while the feedback of
magnetic dissipation onto the thermal reservoir is neglected. Here, we establish a rigorously self-consistent bidirectional magneto-thermal coupling model by integrating the
stochastic Landau-Lifshitz-Gilbert (sLLG) equation with a generalized heat transfer equation. In this closed-loop framework, the local temperature acts as a dynamical variable, and the damping-induced dissipation alongside
stochastic work dynamically feeds back into the thermal bath as localized heat sources. Utilizing Ito
stochastic calculus, we analytically prove that this coupled system strictly obeys the first law of thermodynamics and spontaneously recovers the correct Boltzmann statistics at
equilibrium. Spatially resolved micromagnetic simulations further validate the energy exchange mechanism, capturing the finite-bath temperature reduction induced by spatial variation of
magnetic moments and the modified density of states under exchange interactions. This bidirectional framework provides a robust microscopic foundation for investigating complex nonequilibrium magneto-thermal dynamics, such as the unidirectional
spin-wave heat conveyer effect, paving the way for advanced
spin-caloritronic applications.
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Materials Science
Conditional spinodal decomposition in Li-Mg anodes for lithium metal batteries
Leonardo Shoji Aota, Aubin Leray, Yuqi Liu et al. (+14 more)
The development of batteries with high energy density, short charging times and use of sustainable materials is critical for decarbonization. Magnesium (Mg)-based anodes for lithium (Li) metal batteries promote homogeneous Li plating, thereby avoiding the formation of Li dendrites that cause short
circuits and battery failure. However, microstructural modifications induced by Li-alloying and their influence on battery operation remain elusive. Here, we unveil the previously unknown formation of an ordered B2 phase, which creates a conditional spinodal decomposition with the e̱ta}-body-centered cubic phase. Chemical fluctuations characteristic of spinodal decomposition give rise to uniformly dispersed Li-rich e̱ta}-BCC and Li-poor B2 continuous interconnected phases, with the former providing a fast
diffusion pathway for Li
diffusion towards the anode, hence decreasing the propensity for dendrite formation at elevated current density. This is achieved using Earth-abundant and inexpensive Mg.
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All authors Leonardo Shoji Aota, Aubin Leray, Yuqi Liu, Frederic de Geuser, Chanwon Jung, Shyam Katnagallu, Tim M. Schwarz, Alisson Kwiatkowski da Silva, Júlio César Pereira dos Santos, Eric Marchezini Mazzer, Poonam Yadav, Christoph Freysoldt, Frank Stein, Yug Joshi, Se-Ho Kim, Dierk Raabe, Baptiste Gault
Quantum Gases
Continuum Neural Momentum Eigenstate for Variationally Solving Quasiparticles
David D. Dai and Marin Soljačić
We design the first neural
quantum state for continuum particles that, for any chosen allowed momentum $\mathbf{k}$, is by construction an exact eigenstate of total momentum with
eigenvalue $\mathbf{k}$. Our architecture, EVE, enables off-the-shelf VMC to solve for momentum-sector ground states. We test EVE on 2D
bosons with mutual $1/r$ interactions, finding that a single unified ansatz is capable of describing four qualitatively different states: superfluid, roton,
crystal, and
phonon. At different densities, we extract the underlying phase of matter from the dispersion's shape. At $r_s = 20.0$, we see the roton minimum at finite $k$ expected of a superfluid. At $r_s = 100.0$, we see striking zone folding indicative of crystalline order, with periodically spaced minima representing floating
crystals connected by
phonon arcs in between. Using density-density correlation functions, we confirm the phase diagnoses and probe the excitations' correlation structures. Finally, we analyze the roton's phase texture and find unexpected multi-particle phase strings, formed when several
vortex dipoles merge, leaving two
vortices connected by a phase slip.
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Mesoscale and Nanoscale Physics
Quantum charge pumping in helical systems: A comparative study of short- and long-range hopping
Leila Eslami, Santanu K. Maiti and Fatemeh Bourbour
Using the Keldysh non-
equilibrium Green's function approach, we investigate charge pumping through a single-stranded helical structure described by a tight-binding model that includes either short-range hopping (SRH) or long-range hopping (LRH). While
quantum pumping has been studied in various low-dimensional systems, the detailed behavior of the spectral current and the pumped dc current in helical geometries in the presence of higher-order electron hopping (beyond nearest neighbors) has not yet been systematically explored. Here, we focus on the interplay between helicity and extended hopping ranges, analyzing how they jointly control the energy-resolved and dc pumped currents under time-periodic end potentials. For LRH, the pumped dc current exhibits pronounced plateau-like regions as a function of chemical potential when energy levels are sparsely spaced – consistent with adiabatic transport – whereas SRH yields more parameter-sensitive currents without clear plateaus. The plateau stability is controlled by the drive frequency: at higher frequencies, Floquet side-band mixing destroys the plateaus, leading to oscillatory currents. The phase dependence remains nearly sinusoidal, and the current vanishes at zero phase lag, confirming the necessity of out-of-phase potentials. Crucially, in helical systems, the decay exponent $(\ell_c)$ acts as an effective structural parameter that can tune both the magnitude and sign of the pumped current, offering a
geometric knob for controlling
quantum pumping. Our findings not only fill a gap in the understanding of spectral and pumped currents in helical systems with extended hopping but also provide tools that can be applied to analyze similar phenomena in other
chiral or quasi-one-dimensional systems.
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Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Global Control with the Tavis-Cummings Interaction
Plato Deliyannis and Iman Marvian
We study the controllability of a system of
qubits under global control, where control pulses act identically on all
qubits. Specifically, we consider a collection of
qubits identically coupled to a single bosonic mode, or harmonic oscillator, via the Jaynes-Cummings interaction. This collective coupling, known as the Tavis-Cummings (TC) interaction, has been realized in several
quantum computing platforms, including superconducting and atomic
qubit systems. Although the
qubits do not interact directly with one another, they can become entangled through their common coupling to the bosonic mode. We characterize the group of
unitaries that can be implemented on the joint
Hilbert space of the
qubits and bosonic mode using the TC interaction together with a global $z$ field $J_z$, corresponding to identical z rotations on all
qubits. We show that for n>2
qubits the set of realizable
unitaries is restricted by an "accidental"
symmetry of the TC
Hamiltonian, distinct from its "standard" U(1) and permutational
symmetries. On the other hand, we find that the
Hamiltonian $J_z^2$ breaks this accidental
symmetry and, together with the TC interaction and $J_z$, achieves semi-universality: it allows the implementation of arbitrary
unitaries that respect permutational and U(1)
symmetry, up to certain constraints on the center of the group. In a companion paper, we further analyze this remarkable accidental
symmetry and show that it can be understood through Schwinger's bosonic model of angular momentum.
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Materials Science
Leveraging rapid sintering to retain metastable zirconia in copper
Wangshu Zheng, Xi Chen, Xuyang Feng et al. (+6 more)
Cermets combining metastable ceramics and ductile metals promise superior toughness and strength. However, retaining metastability often requires high-temperature sintering that coarsens microstructures and relaxes
matrix constraint. Here we introduce an ultrafast high-temperature sintering (UHS) strategy to overcome this trade-off in zirconia-copper cermets. By applying Joule heating at around 100 degrees C per second to 900 degrees C with only a 20 second hold, we obtained cermets containing up to 50 weight percent of metastable austenite in zirconia at room temperature within a fine-grained and homogeneous microstructure. The rapid sintering kinetically favors semi-thermal austenite formation while suppressing copper grain growth and
matrix relaxation, thereby stabilizing the high-temperature phase and simultaneously preserving microstructural refinement. This approach offers significant potential for copper-based composites in applications such as transformation toughening, self-healing, and crack detection.
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All authors Wangshu Zheng, Xi Chen, Xuyang Feng, Aiji Zou, Andrew Yun Ru Ng, Xiaoqing Wang, Zhili Dong, Qiang Guo, Chee Lip Gan
Mesoscale and Nanoscale Physics · Cross-listed from quant-ph
Accidental Symmetry in the Tavis-Cummings Model via the Schwinger Boson Representation
Plato Deliyannis and Iman Marvian
The Jaynes-Cummings (JC)
Hamiltonian is a paradigmatic model of light-matter interaction and, more generally,
qubit-
boson interactions, widely used across atomic, optical, and superconducting
qubit platforms. In the multi-
qubit setting, where n
qubits are identically coupled to a single
boson mode, this interaction is known as the Tavis-Cummings (TC)
Hamiltonian. The structure of the TC model is usually understood in terms of two standard
symmetries: permutation invariance of the
qubits and a U(1)
symmetry associated with conservation of the total excitation number. Here we identify an additional, independent "accidental"
symmetry of the TC
Hamiltonian and construct the corresponding conserved observable. We show that, for n>2
qubits, this
symmetry imposes strong constraints on the realizable
unitary transformations. These constraints persist in the presence of the global $J_z$
Hamiltonian, but are removed by adding $J_z^2$, even though $J_z^2$ preserves both permutation invariance and the U(1)
symmetry. Finally, we explain the origin of this previously unnoticed
symmetry using Schwinger's
boson representation of angular momentum. These restrictions have important implications for controllability of the TC system and for its applications to
quantum computing, which are investigated further in a companion paper.
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Materials Science
A wrong ground-state structure of HfO$_2$ predicted by machine-learning interatomic potentials based on the PBE functional
Shuqi Tang, Jinchen Wei, Kang Wang et al. (+4 more)
Machine-learning interatomic potentials (MLIPs) have become powerful tools for material simulations. Many MLIPs are trained based on density functional theory (DFT)
datasets generated with the Perdew-Burke-Ernzerhof (PBE) exchange-correlation functional. Using a PBE-based MLIP for HfO2, we identify a previously unreported low-energy I41/amd structure, which is predicted to be more stable than the well-known ground-state structure, the monoclinic P21/c structure. Since experiments show clearly that HfO2 takes the P21/c structure as the ground state, this is obviously a wrong prediction. Unfortunately, the same prediction is also made by widely used PBE-based foundation models such as NequIP-OAM-L and MatterSim-v1-5M. Comparisons among different DFT functionals show that this error originates from the PBE functional, which overstabilizes low-density structures containing sixfold Hf-O octahedral units, such as the I41/amd and Pbcn phases. The error also affects the calculated energy landscapes and barrier heights along ferroelectric HfO2 polarization switching paths when there are large
lattice relaxations. Fortunately, the error can be largely suppressed by other functionals such as PBEsol and local density approximation. Our study serves as a warning about the impact of errors in exchange-correlation functional approximations on the reliability of MLIP simulations of
crystal structures and phase transitions.
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All authors Shuqi Tang, Jinchen Wei, Kang Wang, Junjie Zhou, Yihan Zhang, Menglin Huang, Shiyou Chen
Statistical Mechanics
When proofreading improves both speed and accuracy
Arup Biswas and L. Mahadevan
Proofreading is generally thought to improve accuracy at the expense of speed. We show that this trade-off can be reversed in
stochastic processes with long-lived stalled states. Using a non-Markovian renewal framework, we derive exact expressions for the error rate and completion time under proofreading for arbitrary stall-time distributions. Our analysis reveals that fluctuations in stall durations, rather than their mean alone, determine whether proofreading can simultaneously increase speed and accuracy. In the limit of strong stalling, this regime emerges when the coefficient of variation of the stall time exceeds a threshold set by the intrinsic error rate. These results provide a general criterion for proofreading in systems ranging from self-assembly and
polymer replication to immune recognition and other nonequilibrium information-processing systems.
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Materials Science
Molecular reference corrections for quantum Monte Carlo adsorption energies
Roman Fanta and Michal Bajdich
Accurate surface thermochemistry requires balanced error cancellation between extended slabs and molecular reference states. This balance can fail whenever the electronic-structure error is not transferable across the chemically distinct species entering a thermodynamic cycle. Here we examine this problem in single-determinant fixed-node
diffusion Monte Carlo (SD-FNDMC) for oxygen-reduction intermediates on Pt(111) and selected CO-reduction intermediates on Cu(111). Gas-phase thermochemistry is used to diagnose the reference-state imbalance, and a hybrid cycle is introduced to separate slab–adsorbate binding from molecular formation. The hybrid cycle keeps the surface binding term at the SD-FNDMC level, where cancellation is expected to be most favorable, and replaces the molecular formation contribution with a
benchmark coupled cluster reference. For Pt(111), the resulting correction is small for O and OH but larger for OOH, while the geometry-matched refinement gives only a secondary correction. Applying the same cycle to $^\ast$CHO and $^\ast$COH adsorption on Cu(111) gives corrections of opposite sign, showing that the bias is controlled primarily by the electronic structure of the corresponding HCO and COH molecular references rather than by adsorbate geometry alone. This decomposition identifies molecular reference imbalance as a separable source of error in SD-FNDMC surface thermochemistry and reduces the corresponding bias without modifying the SD-FNDMC slab-binding contribution.
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Superconductivity
Revealing nonvolatile behaviors in magneto-thermal switching using microstructure-controlled superconducting composites
Keigo Ito, Yui Sakamoto, Hossein Sepehri-Amin et al. (+12 more)
Thermal conductivity in a conductor changes by the application of an external
magnetic field, which functions as a magneto-thermal switch. For
superconductors, a large magneto-thermal switching can occur through a superconducting-to-normal conducting phase transition due to the change in the electron contribution in thermal conductivity. Arima et al. recently reported a nonvolatile nature of the magneto-thermal switching for superconducting solders, which consist of phase-separated Sn and Pb domains. Although they clarified that
magnetic flux trapping is required to induce the nonvolatile magneto-thermal switching, a rule for such material design is still unclear. Here, we investigate the microstructure dependence of magneto-thermal switching in superconducting Sn/Pb multilayered composites, which are created by an accumulative roll bonding method. The thickness of each layer, that is the scale of microstructure, can be systematically controlled by the repetition number of roll bonding while the whole sample size and average composition are unchanged. We find that, as the formation of micro-scaled Sn domains proceeds by increasing the repetition number, a nonvolatility in the magneto-thermal conductivity gradually appears in correlation with the remanent magnetization. This study directly confirms that the inclusions with a size comparable to or less than the
magnetic vortex in superconducting
matrix is essential for
magnetic flux trapping, enabling the nonvolatile magneto-thermal switching in superconducting composites.
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All authors Keigo Ito, Yui Sakamoto, Hossein Sepehri-Amin, Yuto Watanabe, Poonam Rani, Kumpei Imamura, Takamasa Hirai, Keisuke Hirata, Shunsuke Mori, Yusuke Nakanishi, Kenichiro Hashimoto, Takasada Shibauchi, Yoshikazu Mizuguchi, Ken-ichi Uchida, Fuyuki Ando